In recent years, compositions which are cured by irradiation with active rays such as ultraviolet rays have been used in a wide variety of fields, such as fields of coating materials, UV-curing or thermosetting coating materials, molding materials, adhesives, inks, resists, optical materials, photo-shaping materials, printing board materials, dental materials, polymer cell materials and polymer raw materials. For example, they have been used for optical materials, such as coating materials for optical lenses and films, cladding materials for optical fibers, and optical adhesives for optical fibers or optical lenses.
As such curable compositions, compositions which are cured by lower energy, compositions which are cured more rapidly, compositions capable of forming more precise and finer patterns, compositions having deeper cure depth and compositions having higher storage properties have been desired according to the requirements of higher functions in the above-mentioned various fields of optical materials, electron materials, etc., and levels of requirements of various properties, e.g., optical properties such as transmittance and refractive index, adhesion to substrates and heat resistance, have become higher.
The photosensitive compositions are mainly constituted of a photopolymerization initiator, a compound having an ethylenically unsaturated bond which is cured by polymerization reaction, and various additives, and according to the use purpose, various kinds of components are employed. The photopolymerization initiator is selected based on its photosensitive wavelength or polymerization initiation properties, the compound having an ethylenically unsaturated bond and the additives are selected based on polymerizability or properties of a cured product desired, and they are used in combination.
As one of such photosensitive compositions, a curable composition containing a thiol compound is known. The curable composition of this kind is cured by irradiation with light in a short period of time of several seconds to several minutes after the compound containing a polyethylenically unsaturated double bond and the thiol compound undergo radical polymerization. Such a conventional polyene-polythiol-based photo-curing composition is excellent in processability and curability, but on the other hand, the composition has poor stability, and when the composition is kept in a liquid state before use, it is thickened and liable to suffer gelation. Moreover, there is a problem that a photo-cured product prepared from the composition having been kept in such a state has low heat resistance.
For example, when such a photosensitive composition containing straight-chain thiol as described in patent documents 1 and 2 is used as a photosensitive composition used for a color filter, the resulting photosensitive composition is sometimes improved in sensitivity but has insufficient storage stability, so that it is difficult to secure sufficient sensitivity when the composition is used.
In order to obtain a photosensitive composition having excellent storage stability with maintaining sensitivity of the photosensitive composition, the present inventors have paid attention to that selection of a photopolymerization initiator composition is important and particularly to that there is a problem in thermal reactivity of a thiol compound used as one component of the photopolymerization initiator composition.
Patent document 1: Japanese Patent Laid-Open Publication No. 253815/1998
Patent document 2: Japanese Patent Laid-Open Publication No. 249822/2000